Methods and Systems for Obtaining Aerial Imagery for Use in Geospatial Surveying

1. A computer-implemented method of optimising aerial observation positions for capturing aerial images of a geographical area, the method comprising: receiving a set of initial aerial observation positions corresponding to the geographical area; receiving a three-dimensional digital surface model representative of a surface of the geographical area, wherein the digital surface model comprises a plurality of pixels; determining whether the plurality of pixels are visible to an image capture device located at each of the set of initial aerial observation positions in dependence on a field of view of the image capture device and a configuration of the digital surface model, wherein for each initial aerial observation position the plurality of pixels are analysed to identify a subset of pixels located within the field of view of the image capture device located at the respective initial aerial observation position, wherein identifying the subset of pixels comprises: (i) calculating a pixel angle from each pixel in the plurality of pixels to the respective initial aerial observation position; and (ii) comparing the pixel angle to a minimum angle calculated in dependence on the field of view of the image capture device located at the respective initial aerial observation position, wherein when the pixel angle is more than or equal to the minimum angle, the pixel is identified as part of the subset of pixels; calculating, for each pixel in the plurality of pixels, a number of the initial aerial observation positions, wherein the pixel is visible to the image capture device when the image capture device is located at each of the number of the initial aerial observation positions; and generating a set of optimised aerial observation positions in dependence on said calculation of the number of the initial aerial observation positions.

2. A method according to claim 1 , wherein method further comprises analysing the set of pixels to determine whether the subset of pixels are visible to the image capture device located at the respective initial aerial observation position, wherein the analysing comprises: generating a path from each pixel in the subset of pixels to the respective initial aerial observation position; and determining whether the pixel is visible to the image capture device at the respective initial aerial observation position in dependence on a trajectory of said path.

3. A method according to claim 2 , wherein generating the path from each pixel in the subset of pixels comprises: calculating a direction vector from the pixel to the respective initial aerial observation position; and iteratively moving along the direction vector towards the respective initial aerial observation position.

4. A method according to claim 2 , wherein a pixel is determined to be visible to the image capture device at the respective initial aerial observation position if the path does not intersect a further pixel of the digital surface model and/or the path reaches a predetermined height above the digital surface model.

5. A method according to claim 4 , wherein the predetermined height is at least 300 meters.

6. A method according to claim 1 , further comprising generating an image map of the geographical area indicating the number of initial aerial observation positions calculated for each pixel in the plurality of pixels.

7. A method according to claim 1 , wherein generating the set of optimised aerial observation positions comprises: identifying one or more pixels from the calculating, wherein the calculated number of initial aerial observation positions for the one or more pixels is less than a threshold value; and determining the set of optimised aerial observation positions in dependence on the identified one or more pixels.

8. A method according to claim 7 , wherein the threshold value is two.

9. A method according to claim 7 , wherein the set of optimised aerial observation positions are such that the one or more pixels are visible to the image capture device when located at a number of the optimised aerial observation positions above the threshold value.

10. A method according to claim 1 , wherein generating the set of optimised aerial observation positions comprises at least one of: adjusting a coordinate of one or more of the initial aerial observation positions; and adding one or more further aerial observation positions to the set of initial aerial observation positions.

11. A method according to claim 1 , wherein the field of view is calculated based on one or more physical parameters of the image capture device.

12. A method of aerial imaging, the method comprising capturing one or more images of a geographical area at a plurality of optimised aerial observation positions generated according to a method comprising: receiving a set of initial aerial observation positions corresponding to the geographical area; receiving a three-dimensional digital surface model representative of a surface of the geographical area, wherein the digital surface model comprises a plurality of pixels; determining whether the plurality of pixels are visible to an image capture device located at each of the set of initial aerial observation positions in dependence on a field of view of the image capture device and a configuration of the digital surface model, wherein for each initial aerial observation position the plurality of pixels are analysed to identify a subset of pixels located within the field of view of the image capture device located at the respective initial aerial observation position, wherein identifying the subset of pixels comprises: (i) calculating a pixel angle from each pixel in the plurality of pixels to the respective initial aerial observation position; and (ii) comparing the pixel angle to a minimum angle calculated in dependence on the field of view of the image capture device located at the respective initial aerial observation position, wherein when the pixel angle is more than or equal to the minimum angle, the pixel is identified as part of the subset of pixels; calculating, for each pixel in the plurality of pixels, a number of the initial aerial observation positions, wherein the pixel is visible to the image capture device when the image capture device is located at each of the number of the initial aerial observation positions; and generating a set of optimised aerial observation positions in dependence on said calculation of the number of the initial aerial observation positions.

13. A system comprising: a processor; and non-transitory memory storing one or more instruction(s) arranged such that when executed the processor is caused to perform a method of optimising aerial observation positions for capturing aerial images of a geographical area, wherein the processor is caused to: receive a set of initial aerial observation positions corresponding to the geographical area; receive a three-dimensional digital surface model representative of a surface of the geographical area, wherein the digital surface model comprises a plurality of pixels; determine whether the plurality of pixels are visible to an image capture device located at each of the set of initial aerial observation positions in dependence on a field of view of the image capture device and a configuration of the digital surface model, wherein for each initial aerial observation position the plurality of pixels are analysed to identify a subset of pixels located within the field of view of the image capture device located at the respective initial aerial observation position, wherein identifying the subset of pixels comprises: (i) calculating a pixel angle from each pixel in the plurality of pixels to the respective initial aerial observation position; and (ii) comparing the pixel angle to a minimum angle calculated in dependence on the field of view of the image capture device located at the respective initial aerial observation position, wherein when the pixel angle is more than or equal to the minimum angle, the pixel is identified as part of the subset of pixels; calculate, for each pixel in the plurality of pixels, a number of the initial aerial observation positions, wherein the pixel is visible to the image capture device when the image capture device is located at each of the number of the initial aerial observation positions; and generate a set of optimised aerial observation positions in dependence on said calculation of the number of the initial aerial observation positions.

14. A system according to claim 13 , wherein the processor is further caused to analyse the set of pixels to determine whether the subset of pixels are visible to the image capture device located at the respective initial aerial observation position, wherein the analysing comprises: generating a path from each pixel in the subset of pixels to the respective initial aerial observation position; and determining whether the pixel is visible to the image capture device at the respective initial aerial observation position in dependence on a trajectory of said path.

15. A system according to claim 14 , wherein the processor is configured to generate the path from each pixel in the subset of pixels by: calculating a direction vector from the pixel to the respective initial aerial observation position; and iteratively moving along the direction vector towards the respective initial aerial observation position.

16. A system according to claim 14 , wherein a pixel is determined to be visible to the image capture device at the respective initial aerial observation position if the path does not intersect a further pixel of the digital surface model and/or the path reaches a predetermined height above the digital surface model.

17. A system according to claim 13 , wherein the processor is caused to generate the set of optimised aerial observation positions by: identifying one or more pixels from the calculating, wherein the calculated number of initial aerial observation positions for the one or more pixels is less than a threshold value; and determining the set of optimised aerial observation positions in dependence on the identified one or more pixels.

18. A system according to claim 17 , wherein the set of optimised aerial observation positions are such that the one or more pixels are visible to the image capture device when located at a number of the optimised aerial observation positions above the threshold value.

19. A system according to claim 13 , wherein the processor is caused to generate the set of optimised aerial observation positions by at least one of: adjusting a coordinate of one or more of the initial aerial observation positions; and adding one or more further aerial observation positions to the set of initial aerial observation positions.

20. A system according to claim 13 , wherein the field of view is calculated based on one or more physical parameters of the image capture device.